from ongoing plate tectonics, which is the geological
process in which Earth’s large basaltic plates, some
bearing continents and islands, move in relation to
one another because of heat generated from inside
the planet itself. Plate tectonics creates vicariance on
a global scale. Similarly, island floras and faunas are
unique because following random colonization (from
a mainland source) by various organisms, evolution
occurred in isolation from mainland influences.
The unique floras and faunas of the Hawaiian and
Galápagos Islands illustrate this point.
On a continent, a physical barrier separating species
could be a mountain range, such as the vast Andes chain
in South America; a broad river, like the Amazon; or
perhaps a desert, such as the Atacama of western Peru
and Chile. On a broader scale, oceans form barriers
between the continents and around islands. Allopatry
imposed by vicariance creates a physical barrier to
gene exchange, and that triggers speciation (plate 8- 4).
When a species’ evolutionary history, its very
genealogy, is unique to a given region, and the species
is found only in that region, it is termed endemic.
Endemism is typically common among island species
because of the relative isolation of islands (plates 8- 5–
7). For example, of the approximately 100 resident bird
species in the Bahama Islands, three are endemic. The
island of Cuba contains 23 species of endemic birds.
The Galápagos archipelago, isolated from Ecuador by
about 1,000 km (620 mi) of ocean, is legendary for its
unique assemblage of endemic plants, birds, and reptiles,
which inspired Charles Darwin to begin thinking about
the possible evolutionary implications of endemism
after he visited the islands in 1835 (plate 8- 8).
Endemism is also a common component of
continental areas, where it may take two forms. One
of these is taxonomic endemism. The woodcreepers
and ovenbirds of the family Furnariidae represent an
endemic family, found only in the Neotropics (plate 8-
9). Of course, this type of endemism applies at various
taxonomic levels: there are endemic families, endemic
genera, and endemic species.
Another form of endemism is regional endemism,
which occurs when a specific area within a region
contains a variety of endemic species, many not
closely related. For example, nine distinct areas of
avian regional endemism are recognized in Ecuador
(plate 8- 10). Such centers of regional endemism are
of particular conservation concern, since they contain
unique arrays of species.Figure 8– 1. Areas of postulated endemism in northern South
America. From Cracraft 1985. Reprinted with permission
from Kricher, John. Tropical Ecology. Princeton, NJ: Princeton
University Press, 2011.Figure 8– 2. Areas of postulated endemism for Amazonia and
the Andes Mountains. From Cracraft 1985. Reprinted with
permission from Kricher, John. Tropical Ecology. Princeton, NJ:
Princeton University Press, 2011.Plate 8- 10. The 20 cm (8 in) long Toucan- Barbet (Semnornis
ramphastinus) is one of 44 bird species endemic to the
western slope of the Andes in Ecuador. A country with a total
area about equal to that of the state of Nevada, Ecuador has
nine unique areas of avian endemism that account for 243
species in total. Photo by Steve Bird.chapter 8 evolutionary cornucopia 115